If you see S3 issue for Intel P55 series motherboard, please refer the following trouble shooting procedures for solution.
(1) Unplug power cord.
(2) Unplug all power cable and CMOS battery.
(3) Refer user manual to clear CMOS by jumper JCMOS1.
(4) Plug all the power cable and CMOS battery back to motherboard.
(5) Boot up system, then enter BIOS CMOS setup to Load Optimized default setting. Set S3 function and press F10 to save CMOS setting.
(6) Re-check S3 function.
(7) If S3 issue persist, please go back to procedure (1) and do the procedure again.
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